/*
 * Microsoft research Asia, Internet Graphics Group
 * Copyright (c) 1987-2003 Microsoft Corporation
 *	
 *	  History:
 *	  Created on 06/01/2003 by Ligang Liu, i-ligliu@microsoft.com
 *
 *
 * This file is part of PolyMaker, a software that create polygon-based
 * 2D vector graphics. The software is designed for generating WF objects
 * for testing different 2D shape blending algorithms in Morphos system.
 *
 */

/*
	Removing flicker from an MFC application is well-covered territory. You can find the 
	topic addressed in books, and on-line. However, the techniques presented are somewhat 
	complicated and are usually difficult to add to an existing application. One often-presented 
	technique is called double buffering. Double buffering allows the new screen to be drawn in 
	off-screen memory, and then the completed screen is bit-blited back onto the physical screen. 

	This is a class called CMemDC that encapsulates most of the issues associated 
	with writing to off-screen buffers. 
	from:
		http://www.codeproject.com/gdi/flickerfree.asp

	Adding CMemDC to an existing application is nearly trivial. Modifying an MFC 
	Application to use CMemDC:
	1. Add the file memdc.h in your project. 
	2. Add the line #include "memdc.h" to stdafx.h. 
	3. Add a windows message handler for WM_ERASEBKGND. 
		BOOL CExampleView::OnEraseBkgnd(CDC* pDC) 
		{
			//return CView::OnEraseBkgnd(pDC);
			return FALSE;
		}
	4. Change your OnDraw code to the following: 
		void CExampleView::OnDraw(CDC* dc)
		{
			CMemDC pDC(dc);
			CExampleDoc* pDoc = GetDocument();
			ASSERT_VALID(pDoc);
			// TODO: add draw code for native data here - use pDC 
			//as the device context to draw to
		}
*/


#ifndef _MEMDC_H_
#define _MEMDC_H_

//////////////////////////////////////////////////
// CMemDC - memory DC
//
// Author: Keith Rule
// Email:  keithr@europa.com
// Copyright 1996-2002, Keith Rule
//
// You may freely use or modify this code provided this
// Copyright is included in all derived versions.
//
// History - 10/3/97 Fixed scrolling bug.
//                   Added print support. - KR
//
//           11/3/99 Fixed most common complaint. Added
//                   background color fill. - KR
//
//           11/3/99 Added support for mapping modes other than
//                   MM_TEXT as suggested by Lee Sang Hun. - KR
//
//           02/11/02 Added support for CScrollView as supplied
//                    by Gary Kirkham. - KR
//
// This class implements a memory Device Context which allows
// flicker free drawing.

class CMemDC : public CDC {
private:	
	CBitmap		m_bitmap;		// Offscreen bitmap
	CBitmap*	m_oldBitmap;	// bitmap originally found in CMemDC
	CDC*		m_pDC;			// Saves CDC passed in constructor
	CRect		m_rect;			// Rectangle of drawing area.
	BOOL		m_bMemDC;		// TRUE if CDC really is a Memory DC.
public:
	
	CMemDC(CDC* pDC, const CRect* pRect = NULL) : CDC()
	{
		ASSERT(pDC != NULL); 

		// Some initialization
		m_pDC = pDC;
		m_oldBitmap = NULL;
		m_bMemDC = !pDC->IsPrinting();

		// Get the rectangle to draw
		if (pRect == NULL) {
			pDC->GetClipBox(&m_rect);
		} else {
			m_rect = *pRect;
		}

		if (m_bMemDC) {
			// Create a Memory DC
			CreateCompatibleDC(pDC);
			pDC->LPtoDP(&m_rect);

			m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());
			m_oldBitmap = SelectObject(&m_bitmap);

			SetMapMode(pDC->GetMapMode());

			SetWindowExt(pDC->GetWindowExt());
			SetViewportExt(pDC->GetViewportExt());

			pDC->DPtoLP(&m_rect);
			SetWindowOrg(m_rect.left, m_rect.top);
		} else {
			// Make a copy of the relevent parts of the current DC for printing
			m_bPrinting = pDC->m_bPrinting;
			m_hDC       = pDC->m_hDC;
			m_hAttribDC = pDC->m_hAttribDC;
		}

		// Fill background 
		FillSolidRect(m_rect, pDC->GetBkColor());
	}
	
	~CMemDC()	
	{		
		if (m_bMemDC) {
			// Copy the offscreen bitmap onto the screen.
			m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
				this, m_rect.left, m_rect.top, SRCCOPY);			
			
			//Swap back the original bitmap.
			SelectObject(m_oldBitmap);		
		} else {
			// All we need to do is replace the DC with an illegal value,
			// this keeps us from accidently deleting the handles associated with
			// the CDC that was passed to the constructor.			
			m_hDC = m_hAttribDC = NULL;
		}	
	}
	
	// Allow usage as a pointer	
	CMemDC* operator->() 
	{
		return this;
	}	

	// Allow usage as a pointer	
	operator CMemDC*() 
	{
		return this;
	}
};

#endif